#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep1(i, n) for (int i = 1; i < (int)(n + 1); i++)
using ll = long long;
using P = pair<int, int>;
using Graph = vector<vector<int>>;

int main(){
    int n; cin >> n;
    vector<int> v(n, 0);
    rep(i, n)cin >> v[i];

    vector<vector<int>> dp(2, vector<int>(n, 0));
    dp[1][0] = v[0];

    rep1(i, n-1){
        dp[0][i] = max(dp[1][i-1], dp[0][i-1]);
        dp[1][i] = max(dp[1][i-1], dp[0][i-1]+v[i]);
    }

    cout << max(dp[0][n-1], dp[1][n-1]) << endl;
}